In environments such as magnetic resonance imaging (MRI) rooms in medical facilities, there can exist high magnetic fields which can interfere with other electrical systems such as the lighting in the room (e.g., light flicker). It is also the case that equipment such as that found in lighting systems may cause unwanted artifacts (from the radio frequency interference (RFI) emitted by the lighting systems) in the data (corrupted data) being gathered by the MRI system itself. Both of these effects are problematic in such a facility.
The magnetic fields in such facilities may be quite high. For example, in an MRI room having a 3-Tesla MRI system, magnetic field strengths may be as high as 300V/meter or more and magnetic field gradients as high as 820 gauss/cm or more are possible. The frequencies of interest in the signals being measured are in the megahertz range. For a 3-Tesla system, the upper range of such frequencies are up to on the order of 128 MHZ.
LED lighting systems are becoming important for many lighting application because, among other advantages, such systems consume much less power than several other types of lighting systems. There are other advantages as well, such as the fact that incandescent lamps may have extremely short operating lives in such high-magnetic field environments. Thus, for these and other reasons, it is desirable to be able to install LED-based lighting in environments such as MRI rooms and that such systems not be affected by the high fields or disturb the data-taking process in any way. Often the use of dimmer circuitry can be an important source of such interference.